Motor endshield assembly for an electronically commutated motor

ABSTRACT

An endshield assembly for an electronically commutated motor includes an endshield, a control assembly, and a power assembly. The endshield includes a plurality of recessed fins on an outer surface, and a substantially flat raised portion on an internal surface. The raised portion is in contact with a thermal pad. The control assembly includes the thermal pad and a control board on which is located a plurality of power transistors. The thermal pad provides thermal contact between the transistors and the endshield to enable the endshield to dissipate heat from the transistors. The transistors include a plurality of leads that extend substantially parallel to the control board which enable the leads to be coated for protection against harsh external environments. The power assembly includes a power board having an insulator positioned between the power board and the control board.

This application is a 371 of PCT US99/14753 filed Jun. 29, 1999, whichis a continuation of U.S. provisional Ser. No. 60/091,257 filed Jun. 30,1998.

BACKGROUND OF THE INVENTION

This invention relates generally to electric motors and moreparticularly, to an endshield assembly for an electric motor.

Known electronically commutated motors have a multi-stage windingassembly and a magnetic assembly associated for relative rotation. Thewinding stages of the multi-stage winding assembly have a presetenergization sequence that includes at least one unenergized windingstage in which an induced back EMF appears. When integrated over time toa predetermined value, the induced back EMF indicates the instant atwhich the relative angular position between the multi-stage windingassembly and the magnetic assembly is suitable for the sequentialcommutation of the next winding stage.

The electronic circuitry for an electronically commutated motorgenerally includes a power circuit, a regulating circuit, and a controlcircuit. The power circuit has solid state switching devices forcommutating the power supplied to the electronically commutated motor toeffect its energization. The regulating circuit has various solid statecomponents for maintaining the power supplied to the electronicallycommutated motor generally constant. The control circuit has varioussolid state components for controlling the conductivity of the switchingdevices.

Some of the solid state components for an electronically commutatedmotor, e.g., transistors, need to be relatively large to accommodate thecurrents that must pass trough them. Large transistors can produce asizable amount of heat that should be dissipated from the transistors inorder to keep them functioning properly. It is well known in the artthat to promote heat dissipation, the electronic circuitry for anelectronically commutated motor can be positioned adjacent an outersurface of an endshield of the motor. However, this increases costssince another compartment is needed to protect the electronic circuitry.

Accordingly, it would be desirable to provide a mounting arrangement forthe electronic components of an electronically commutated motor thatprovides good heat dissipation without significantly increasing the costof the motor. Additionally, it would be desirable to eliminate theadditional compartment needed to protect the electronic circuitry.

BRIEF SUMMARY OF THE INVENTION

Electronically commutated motors are well known, such as the motordescribed in U.S. Pat. No. 5,006,744, which patent is assigned to thepresent assigned and hereby incorporated herein, in its entirety, byreference.

In an exemplary embodiment of the invention, a motor endshield assemblyfor an electronically commutated motor includes an endshield having aninner surface and an outer surface, with the outer surface including aplurality of recessed fins. The endshield assembly according to oneembodiment of the present invention includes a control assembly and apower assembly mounted thereto. The control assembly includes a controlboard having a plurality of power transistors. The internal surface ofthe endshield includes a substantially flat raised area that is incontact with the control assembly and serves as a heatsink for the powertransistors. The transistors are in contact with a thermal pad locatedbetween the transistors and the endshield. The thermal pad electricallyinsulates the transistors yet still conducts heat from the transistorsto the endshield. The recessed fins are located directly above thesubstantially flat raised portion on the endshield and assist thedissipation of heat from the transistors and endshield to the ambientenvironment.

The power assembly includes a power board having an insulator positionedbetween the power board and the control board. A first spacer extendsbetween the control board and the power board to provide the properspacing therebetween. A plurality of clamp bars are also positionedbetween the power board and the transistors. The clamp bars applypressure to the transistors and keep the transistors in contact with thesubstantially flat raised portion of the endshield. The first spacer andthe clamp bars extend through the insulator. A second spacer extendsbetween the control board and the endshield to provide the properspacing therebetween.

In one embodiment, each power transistor includes a plurality of leadsthat extend substantially parallel to the control board. The leads exita front side of the transistor at a position that is closer to a bottomof the transistor than to a top. The bottom of the transistor is incontact with the control board while the top of the transistor includesa tab that extends from a back side of the transistor parallel to thecontrol board.

With the above described endshield assembly, only one compartment isrequired since the electronic controls are located within the motorhousing. In addition, use of the endshield as a low impedance path todissipate heat from the power devices of the internal electroniccircuitry to the ambient environment provides good thermal performancefor the motor. Also, since the transistor leads are parallel to and awayfrom the control board, the lengths of the leads are much closer to thesurface of the board than in many known control assemblies. The leadsare thus easy to encapsulate and protect from harsh externalenvironments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an endshield assembly in accordance withone embodiment of the present invention;

FIG. 2 is a perspective view of the endshield shown in FIG. 1;

FIG. 3 is a cross section of the endshield shown in FIG. 2 along A—A;

FIG. 4 is a schematic illustration of the thermal pad shown in FIG. 1;and

FIG. 5 is a schematic illustration of the insulator shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an exploded view of an endshield assembly 100 for anelectronically commutated motor (not shown). Endshield assembly 100includes an endshield 102, a control assembly 104, and a power assembly106. Control assembly 104 includes a control board 108, a plurality oftransistors 110, a thermal pad 112, and a spacer 114. In one embodiment,spacer 114 is fabricated from nylon and extends between control board108 and endshield 102. Spacer 114 helps to maintain a predeterminedseparation distance between control board 108 and endshield 102.

Transistors 110 include a front 116, back 118, top 120, bottom 122, anda tab 124. Tab 124 extends from back 118 of transistors 110 and has asurface 126 that is an extension of, and is substantially parallel to,top 120. A plurality of leads 128 extend from front 116 of transistor110. In one embodiment, leads 128 extend substantially parallel tocontrol board 108 and maintain a substantially constant separationdistance between themselves and control board 108. Since leads 128extend from front 116 in a location that is closer to control board 108than to top 120, leads 128 remain relatively close to control board 108throughout their length. Only a small separation distance exists betweenleads 128 and control board 108. The small separation distance allowsconformal coating to easily encapsulate leads 128 which helps to protectthem from damage in harsh environments. The encapsulation of leads 128facilitates reducing failures caused by moisture in the area of highpotential. To insert leads 128 into control board 108, leads 128 must beformed at right angles to transistor 110.

Transistors 110 are capable of producing significant heat depending onthe amount of current that flows through them. The heat should bedissipated from the transistors and the surrounding motor in order toensure proper operation of the motor. In one embodiment, top 120 of eachtransistor 110 is in thermal contact with thermal pad 112. Thermal pad112 electrically isolates transistors 110 and conducts the heatgenerated by transistors 110 away from transistors 110. Thermal pad 112contacts endshield 102 which includes an inner surface (not shown) andan outer surface 130 that has a plurality of recessed fins 132. In oneembodiment, endshield 102 is fabricated from cast aluminum and serves aheatsink for transistors 110. The inner surface of endshield 102includes a substantially flat raised portion (not shown). Thesubstantially flat raised portion is in thermal contact with thermal pad112 and is located directly beneath recessed fins 132. In oneembodiment, recessed fins 132 extend from the substantially flat raisedportion. The heat from transistors 110 travels through thermal pad 112to endshield 102 and is dissipated from recessed fins 132 to the ambientenvironment. Endshield 102 serves as a heat sink to transistors 110 andhelps to dissipate heat from transistors 110 to the ambient environment.This heat dissipation helps reduce stress on transistors 110. Endshield102 further includes a cap plug opening 134 and a cap plug 136 as willbe discussed in more detail below.

Power assembly 106 includes a power board 138, electronic components140, a spacer 142, a plurality of clamp bars 144, and an insulator 146.Insulator 146 is positioned between control board 108 and power board138 and electrically insulates portions of control board 108 fromportions of power board 138. Spacer 142 and clamp bars 144 extendbetween control board 108 and power board 138. Spacer 142 and clamp bars144 facilitate maintaining a predetermined distance between power board142 and control board 108. Spacer 142 and clamp bars 144 extend throughinsulator 146 and are in contact with both control board 108 and powerboard 138. In one embodiment, spacer 142 is fabricated from nylon.

Clamp bars 144 are positioned on an opposite side of power board 138from electronic components 140 and are located between electroniccomponents 140 and transistors 110. Clamp bars 144 apply pressure ontransistors 110 to ensure a good thermal interface between transistors110 and endshield 102.

FIG. 2 is a perspective view of endshield 102. Endshield 102 includes ashaft opening 148 for a rotor bearing (not shown). In one embodiment,outer surface 130 of endshield 102 includes a raised cylinder 150 thatprojects from endshield 102 and surrounds opening 148. Raised cylinder150 includes a resilient ring (not shown) mounted therein. Endshield 102further includes a plurality of bolt openings 152. Bolt openings 152extend through endshield 102 and through bolts (not shown) are insertedtherethrough to mount endshield 102 to the shell of an electronicallycommutated motor (not shown). Cap plug opening 134, as explained above,extends through endshield 102 and allows access to internal components(not shown) during final testing and calibration. Cap plug opening 134permits access to the internal components without having to removeendshield 102. Cap plug 136 (not shown in FIG. 2) covers cap plugopening 134 to protect the internal components.

FIG. 3 is a cross-section view of endshield 102 and illustrates an innersurface 154 that includes a substantially flat raised portion 156.Raised portion 156 is located directly beneath recessed fins 132 and isa component of a thermal pathway between transistors 110 (not shown inFIG. 3) and recessed fins 132. Recessed fins 132 extend from raisedportion 156 to increase the surface area of outer surface 130 whichfacilitates the dissipation of heat from endshield 102. Raised cylinder150 and bold opening 152 are also illustrated in FIG. 3.

FIG. 4 is a schematic illustration of thermal pad 112. In oneembodiment, thermal pad 112 includes angled sides to permit increasedcontact with a portion of endshield 102 (not shown in FIG. 4). Thermalpad 112 has two openings 158 to help secure thermal pad 112 to theendshield.

FIG. 5 is a schematic illustration of insulator 146. Insulator 146includes two openings 160 through which clamp bars 144 (not shown inFIG. 5) extend. Openings 160 are generally rectangular in shape and arepositioned in close proximity to each other. Insulator 146 also includesa shaft opening 162 through which a shaft (not shown) of theelectronically commutated motor extends. Insulator 146 is fabricatedfrom mylar and provides both thermal and electrical insulation.Insulator 146 also includes a spacer opening 164 through which spacer142 (not shown in FIG. 5) extends.

Endshield assembly 100 includes a thermal pathway that allows heat to bedissipated from the interior of endshield assembly 100, to the ambientenvironment. This thermal pathway enables control assembly 104 and powerassembly 106 to be placed within the interior of the electronicallycommutated motor housing. This interior placement eliminates the needfor a separate compartment to house the electronic controls of themotor, and facilitates reducing fabrication costs of the motor. Inaddition, the orientation of the transistor leads enables the leads tobe encapsulated and protected from potentially harsh environmentalconditions.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A motor endshield assembly comprising: an endshield comprising anouter surface, an inner surface having an inner portion, a shaft openingextending therebetween, and a plurality of recessed fins extendingradially outward from said shaft opening towards an outer periphery ofsaid endshield, such that each of said recessed fins extends from saidinner portion to said outer surface; a control assembly in contact withsaid inner surface and positioned directly beneath said recessed fins;and a power assembly connected to said control assembly.
 2. A motorendshield assembly in accordance with claim 1 wherein said inner portionfurther comprises a substantially flat raised portion for contactingsaid control assembly.
 3. A motor endshield assembly in accordance withclaim 2 wherein said recessed fins extend from said substantially flatraised portion.
 4. A motor endshield assembly in accordance with claim 1wherein said control assembly comprises a control board and a pluralityof power transistors connected to said control board.
 5. A motorendshield assembly in accordance with claim 4 wherein said controlassembly further comprises a thermal pad between said power transistorsand said endshield, said thermal pad for transferring heat from saidtransistors to said endshield and for electrically isolating saidtransistors.
 6. A motor endshield assembly in accordance with claim 4wherein each said power transistor comprises a plurality of leads, eachsaid lead extending substantially parallel to said control board.
 7. Amotor endshield assembly in accordance with claim 6 wherein saidtransistors comprise a top surface, a bottom surface, a back, and a tab,said bottom surface contacting said control board, said tab extendingfrom said back along said top surface.
 8. A motor endshield assembly inaccordance with claim 7 wherein said power transistor further includes afront, said leads extend from said front of said power transistors at aposition closer to said bottom surface than to said top surface.
 9. Amotor endshield in accordance with claim 8 wherein said tabs comprisemetal, said tabs contact a thermal pad which provides a thermalinterface to said endshield.
 10. A motor endshield assembly inaccordance with claim 4 wherein said power assembly comprises a powerboard and an insulator positioned between said power board and saidcontrol board.
 11. A motor endshield assembly in accordance with claim10 further comprising: a first spacer extending between said controlboard and said power assembly; a plurality of clamp bars positionedbetween said power assembly and said power transistors, said firstspacer and said claim bars extending through said insulator; and asecond spacer extending between said control board and said endshield.12. A motor endshield assembly in accordance with claim 1 wherein saidendshield is configured as a heatsink.
 13. A motor endshield assembly inaccordance with claim 1 further comprising a cap plug opening extendingthrough said endshield and a cap plug covering said cap plug opening.14. A motor endshield assembly in accordance with claim 1 wherein saidendshield further comprises aluminum.
 15. A motor endshield assembly inaccordance with claim 1 wherein said endshield further comprises aplurality of bolt openings that extend through said endshield forreceiving a through bolt.
 16. A motor endshield for an electronicallycommutated motor, said endshield comprising: a shaft opening configuredto receive a motor shaft; an internal surface comprising a substantiallyflat raised portion; and an external surface comprising a raisedcylindrical portion surrounding said opening and a plurality of recessedfins extending radially outward from said shaft opening towards an outerperiphery of said endshield, such that each of said recessed finsextends from said substantially flat raised portion to said externalsurface.
 17. A motor endshield in accordance with claim 16 furthercomprising a cap plug opening extending through said endshield.
 18. Amotor endshield in accordance with claim 16 further comprising aplurality of recessed openings extending through said endshield, eachsaid recessed opening for receiving a through bolt.
 19. A motorendshield in accordance with claim 16 wherein said endshield furthercomprises aluminum, said endshield configured as a heatsink.
 20. Amethod of assembling a motor endshield assembly for an electronicallycommutated motor, the motor endshield assembly including a controlassembly, a power assembly, and an endshield with an inner surfacehaving an inner portion, an outer surface, a shaft opening extendingtherebetween, and a plurality of recessed fins extending radiallyoutward from the shaft opening towards an outer periphery of theendshield, such that each of the recessed fins extends from the innerportion to the outer surface, said method comprising the steps of:positioning the control assembly in contact with the inner surface ofthe endshield and directly beneath the recessed fins; and connecting thepower assembly to the control assembly.
 21. A method in accordance withclaim 20 wherein the control assembly includes a thermal pad and acontrol board with power transistors connected thereto, said step ofpositioning further comprising the steps of: positioning the powertransistors in thermal contact with the thermal pad; and placing thethermal pad in contact with the endshield.
 22. A method in accordancewith claim 21 wherein the endshield inner surface includes asubstantially flat raised portion, and the endshield outer surfaceincludes a plurality of recessed fins, the recessed fins extending fromthe raised portion, said method of placing the thermal pad comprisingthe step of placing the thermal pad in contact with the substantiallyflat raised portion of the endshield such that the power transistors arein thermal contact with the recessed fins, wherein a thermal pathway isprovided to dissipate heat from the transistors to the recessed fins andthen to the ambient environment.
 23. A method in accordance with claim22 wherein the power assembly includes an insulator, a plurality ofclamp bars, a spacer, and a power board, and wherein said step ofconnecting the power assembly to the control assembly comprises the stepof placing the power assembly in contact with the control board.
 24. Amethod in accordance with claim 23 wherein said method further includesthe step of positioning the clamp bars to apply pressure to thetransistors to enhance the thermal contact between the transistors andthe recessed fins of the endshield.